Page:Proceedings of the Royal Society of London Vol 60.djvu/291

Rh further conclude th a t seven other vertebrae are developed a t the caudal extrem ity, as indicated by th e num ber of vertebral arches and the spinal ganglia in th a t region. W e count, therefore, in all 115 vertebrae, and this is the num ber which can be easily seen in m any specimens of Anguilla vulgaris.

Here I m ust particularly insist th a t I have ascertained in an absolute m anner th a t during th e m etam orphosis of the Muraenoids, the num ber neither of the myomeres nor of the vertebral arches, nor of the spinal ganglia is subjected to any change. The hypurals of Leptocephalus breviostare precisely the same as in the elver of Anguilla vulgaris. The last hypural which is fused w ith the urostyle may present itself as a single piece, or m ay be more or less cleft. These are variations which are m et with also in the elver. J u s t as in the elver, the last bypural but one is always extensively cleft, or, if the expression is preferred, doubled. To the last hypural correspond five rays, w hilst four correspond to the last but one, and one to the last but two, the whole structure being identical w ith th a t found in the elvers of Anguilla vulgaris. Of these ten rays, the eighth, seventh, and sixth are bifid, both in brevirostris and in the elvers of Anguilla vulgaris. Tn the pectoral fin of Leptocephalus brevirostris the definitive rays can be observed, and these are of the sain,e num ber as in the elvers of Anguilla vulgaris. Leptocephalus brevirostris is transparent, and has colourless blood. The red corpuscles are wanting, b u t there are present so-called “ blood-plates ” ( “ Blutplattchen ” in German) sim ilar to those of the inferior vertebrates. The bile is also colourless. This fact is observed in all the other Leptocephali. Leptocephalus brevirostris is, however, the only one which is free from all pigm entation. Correspondingly, the Common Eel is the only species of Murienoid which at the close of metamorphosis is devoid of all trace of larval pigm entation. It was this observation which first led us to the discovery of the relations between Leptocephalus brevirostris and Anguilla vulgaris.

In making transverse sections of Leptocephalus, I found other characters which confirm the relation between it and the Common E e l; for instance, the branchiostegal rays are ten to eleven in number, as is also observed in the elvers of vulgaris. In the Common Eel the well-known lateral branch of th e fifth pair of the cianial nerves exists. I t is also found in Leptocephalus brevirostris. This lateral branch could not be found by Dr. Calandruccio in the other common Mursenoids of Sicily, and is w anting also in the other Leptocephali.

The mucous-canal-sysfem (sensory canals) in the head are already eveloped, partially, in Leptocephalus brevirostris, and are incomp etely developed in the elver. As in the elver, so in Leptocephalus remrostris,the pyloric cceca are wanting. The blind extrem ity of